1. Field of the Invention
The present invention is directed to thermally insulated interfaces. In particular, the present invention is directed to the provision of thermal insulation between the interior of a vessel or conduit and an internal cavity of an adjacent device such as a valve, which forms at least a partial barrier to the flow of heat between the internal cavity and the interior of the vessel or conduit.
2. Description of Background Art
Various sanitary processes require removal of or addition of materials in aseptic fashion. Tanks and conduits are equipped with valves and other process equipment whose process contact surfaces can be cleaned, sanitized or sterilized before being opened to the process. Sterilization, sanitization and even cleaning procedures often require the use of hot media (high temperature steam, for example) to be fed through these devices while they remain attached to, but closed off from direct communication with process vessels or conduits filled with heat-labile process material. When the hot media is fed through these attached devices, a significant amount of heat may be transferred through the device body or attachment device into the vessel or conduit wall and then into the process material or, in cases where these devices include shared walls or integrated process interfaces, heat may be transferred directly from the surfaces of the device body into the process. Process material in the area that is heated may change significantly and irreversibly in character. If a significant amount of material is affected, the production batch may go out of specification and may have to be discarded.
Industrial processes used in the production of foods, beverages, pharmaceuticals, cosmetics and many other products often yield better results if they are carried out under aseptic conditions. Aseptic processing provides added assurance that the final products will have few contaminants, be of more consistent character and of higher quality. To achieve production system asepsis, equipment is usually first cleaned and then sterilized by exposing all surfaces that may come in contact with the process to a hot, moist pressurized environment. This is most frequently and effectively accomplished by supplying clean, hot pressurized steam to all parts of the system that will come in contact with process material before starting the process. Specifically, all vessels, piping, valves, pumps, mechanical agitator seals, filter housings and their filter elements, heat exchangers as well as many other types of equipment are typically cleaned and sterilized.
Once production begins it is usually no longer possible to re-sterilize equipment containing the process material, because the introduction of hot steam would denature many components of the process as well as dilute the process and result in a significant reduction in the overall quality of the product. To protect the aseptic integrity of the process; however, any barrier between equipment containing the production material and another part of the system is usually re-sterilized before being opened to the process. If valves include barriers isolating the process from moving elements and the outside environment (diaphragms or bellows, for instance), re-sterilization is easily conducted by supplying steam through the valve cavity around the barrier element and the valve seal with the process. If a valve, pump or agitator is equipped with sliding or rotating seals (o-rings, packing, etc.) or other types of dynamic non-barrier seals, it is necessary to supply steam through the main cavity through which the process will flow. In addition, it is also desirable to expose the rear non-process side of the seal and adjacent portions of reciprocating or rotating shafts that might come into contact with the process directly or indirectly so that they are also sterile. Because these latter types of seals do not form complete barriers to the process, periodically or continuously steam sterilizing proximal non-process side surfaces can be an effective means of minimizing the risk of microorganism contamination. For this reason many devices that include non-barrier type seals are supplied with double seals wherein there is a process contacting primary seal and a non-process contacting secondary seal. In this way a continuous or periodic live steam barrier to microbial incursion can be established and maintained in the seal housing between the two seals.
The general problem associated with using steam to sterilize, re-sterilize or, where necessary, continuously sterilize (as in the case of an agitator mechanical seal), is the undesirable consequence that adjacent surfaces of equipment also heat up along with the surfaces of equipment intended to be sterilized. Sometimes the adjacent surfaces may also reach sterilization or near-sterilization conditions. While this may not be a problem when sterilizing components that are positioned at a distance from the process, if they are located at or very near an interface with the process, heat can be transferred in significant amounts to the process. Sometimes the amount of heat can be significant enough to affect the process. Furthermore, the temperature of process contact surfaces can rise to levels where process material degrades or forms coatings that may build up on surfaces if heating occurs over an extended period or when component sterilization cycles are repeated many times. Compounding this problem is the difficulty of removing these coatings after a process run. Furthermore, if they are not removed, they pose a threat as contaminants to future process runs.
An obvious alternative approach might be to apply less heat load and try to sterilize at lower temperatures. While this may be an effective alternative approach in some situations, it carries its own risks. A concern would be whether or not the sealing area surface that forms the boundary between process and non-process sides ever reaches sterilization conditions. This surface, shielded by the sealing diaphragm, o-ring, bushing or other sealing element, receives heat indirectly through the walls or the mating sealing element on the side being sterilized. In addition, at the same time, the surface is indirectly cooled by the process on the process side. If the area never reaches sterilization conditions it may serve as a safe haven for contaminating microbes that would be reintroduced into the process when the seal is temporarily broken.
For many industrial processes today, particularly pharmaceutical processes, the exposure of process to excessive temperatures or heat loads, the presence of small amounts of degradants or baked on plaque carried over from earlier batches represent significant threats to quality production. It is desirable, therefore, to find a way to reduce local heat loading and surface temperature excursions at process interfaces that come about as a consequence of heat sanitizing or sterilizing process components.